admin: change path behaviour for the billionth time

URLs are made with app.ExternalURI (now included in window.pages), which
itself should include Base. Also fixed the subfolder being removed from
the url after login.

ts/typings/d.ts

@@ -13,14 +13,18 @@ interface ArrayConstructor {
 }
 
 declare interface PagePaths {
-    // The base subfolder the app is hosted on.
+    // The base subfolder the app is being accessed from.
     Base: string;
+    // The base subfolder the app is meant to be accessed from ("Reverse proxy subfolder")
+    TrueBase: string;
     // The subdirectory this bit of the app is hosted on (e.g. admin is usually on "/", myacc is usually on "/my/account")
     Current: string;
     // Those for other pages
     Admin: string;
     MyAccount: string;
     Form: string;
+    // The "External jfa-go URL"
+    ExternalURI: string;
 }
 
 declare interface GlobalWindow extends Window {